1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus having mechanisms such as a tape loading mechanism adapted for extracting a magnetic tape from a cassette and setting the tape over a predetermined angular range up around a rotary head cylinder, a pinch roller pressing mechanism adapted for pressing a pinch roller to a capstan through the magnetic tape, and so forth.
2. Description of the Prior Art
In a known apparatus of the kind specified above, particularly a video tape recorder, the loading mechanism is operated either in loading mode or in unloading mode by the power of a loading motor which is used also for driving the pinch roller pressing mechanism. In other words, the output power of the loading motor is transmitted not only to the loading mechanism but also to the tape operating mechanisms such as the pinch roller pressing mechanism, braking mechanism, tension arm mechanism and so forth corresponding to various tape operation modes such as forwarding, rewinding, recording, playback or reproduction, still, search and so on, so that these mechanisms are driven commonly by a single motor. According to this arrangement, it is possible to simplify the construction of the apparatus as a whole.
FIGS. 1 to 4 show the mechanism of an example of a conventional video tape recorder. FIG. 1 shows the mechanism in still position, while FIG. 3 shows the same in the playback or reproducing mode. In operation, when a reproducing or playback button 5 is depressed while the apparatus is out of operation (still) as shown in FIG. 1, a slider 59 slides to the right along the base 1 so that the arm 60 is rotated counter-clockwise around a fulcrum constituted by a shaft 60a. The counter-clockwise rotation of the arm 60 causes an arm 61 to rotate clockwise around a fulcrum presented by a pin 61a so that a slider 62 is slid upwardly through the action of a pin 61b. A projection 62c of the slider 62 pushes a switch lever 67' to rotate the same clockwise around a fulcrum constituted by a shaft 73. At the same time, a switch lever 67 is rotated clockwise around a fulcrum constituted by the shaft 73 by the biasing force of the spring 68 with the tapered portion 67a slid in contact with a projection 62 e of the slider 62. As a result, the switch lever 67 presses the actuator 64a of a switch 64, while the switch lever 67' releases the actuator of a switch 65. Consequently, the switch 65 is turned off while the switch 64 is turned on so that a motor 29 is energized to rotate its shaft counter-clockwise. The output torque of the motor 29 is transmitted through a belt 32 to a pulley 31 to rotate the same in counter-clockwise direction. Consequently, a worm 33 coaxially mounted on the pulley 31 is rotated to cause a clockwise rotation of a worm wheel 34 about the axis of a shaft 34b as well as a counter-clockwise rotation of a worm wheel 34' about the axis of a shaft 34b'. The rotation of the worm wheels 34 and 34' drive. links 36 to 38 and 36' to 38' which are connected through pins 34a and 34a' to one ends of springs 35 and 35' provided in guide grooves 34d and 34d' in these worm wheels 34 and 34'. Consequently, pins 39 and 39', which are provided on the other ends of the links 38 and 38', start their movements along U-shaped grooves 40a and 40a' formed in guiding members 40 and 40'. As a result of the movements of the pins 39 and 39', posts 26 and 26' mounted on guide securing members 24 and 24' and cylindrical guiding bodies 27 and 27' catch a magnetic tape 42 in a cassette 54 at two portions of the tape 42 and extract the tape 42 out of the cassette 54 and start movements along grooves 11a and 11b formed in a guide base 11. As the guiding bodies 27 and 27' move, a tension arm 78 is allowed to rotate counter-clockwise around a fulcrum constituted by a shaft 78a by the force of a spring 75 and, as a result of movements of the guide securing members 24 and 24', it is rotated to the position shown in FIG. 4 to limit the path along which the magnetic tape 42 runs. On the other hand, a web-like member 76 exerts a braking force necessary in the recording and reproducing operations to the feeding reel base 10.
As a result of this series of operations, the mechanisms come to take the positions shown in FIGS. 3 and 4. The positions of the posts 27 and 27' on the guide mounting members 24 and 24' are limited due to contact of these posts 27 and 27' with retainer members 41 and 41'. In this state, the magnetic tape 42 runs past the tape guide pins 13, 74 and 14 to make contact with an eraser head 15 and a roller 16 and further to the rotary head cylinder 12 past a cylindrical guiding piece 27 and a correction post 26 and is wound around the rotary cylinder head 12 over a predetermined angle. The tape further runs past a correction post 26' and a cylindrical guiding member 27' and, after making contact with a roller 17 and an audio control head 18, runs into the cassette 54 past a tape guide pin 19 and a capstan 21. Then, the shaft of the motor 29 is further rotated to stretch the springs 35 and 35' in gears 34 and 34' so that the springs 35 and 35' exert a force to press the posts 27 and 27' on the guide securing member 24 and 24' strongly against the retainer members 41 and 41'.
On the other hand, the rotation of the worm wheel 34' brings the pin 34c' on the worm wheel 34' into contact with a loading arm 44 thereby to rotate this arm as shown in FIG. 3. As the arm 44 is rotated clockwise, an arm 45 is pulled out overcoming the force of the spring 53 so that a pinch roller arm 23 is rotated counter-clockwise with respect to the shaft 23a thereby to bring the pinch roller 22 into contact with the capstan 21. Then, as the worm wheel 34' is rotated to move the arm 45 ahead, the arm 50 is rotated clockwise with respect to the shaft 50a so that a spring 51 is slightly tensioned to press the pinch roller 22 onto the capstan 21 with the magnetic tape 42 pinched therebetween.
Referring to FIG. 3, as the pinch roller arm 23 is rotated counter-clockwise, the arm 70 is driven by a pin 23b to rotate clockwise around a fulcrum constituted by a shaft 70a out of engagement with a pin 71a, so that a take-up roller 79 is biased by a spring 72 towards a take-up reel base 9 into driving contact with the same. Meanwhile, the loading arm 44 presses at a portion thereof a projecting piece 67b of the switch lever 67 while rotating the other switch lever 67' counter-clockwise around the fulcrum of the shaft 73, so that the actuator 64a of the switch 64 is released from the pressing force to turn the switch 64 off thereby to stop the power supply to the motor 29. However, due to inertia of the driving system including the rotor of the motor, the worm wheels 34 and 34' are further rotated slightly even after the stop of power supply to the motor 29. This rotation or over-run is limited by the contact of the pin 34c on the worm wheel 34 (see FIG. 3) with the left side 11e of a downward bend 11c of the guide base 11. In addition, since the speed reduction system constituted by the worm 33 and the worm wheels 34 and 34' has a large reduction ratio, the driving system is not reversed even after the motor 29 is stopped by the turning-off of the switch 64 by the loading arm 44, so that the apparatus is held in the recording or playback condition shown in FIGS. 3 and 4.
Thus, in the conventional apparatus, both of the loading mechanism and the operation mechanisms are actuated within a predetermined rotational stroke (maximum 360.degree.) of the worm wheels 34 and 34'. Namely, both of the loading mechanism and the operation mechanisms are driven within a predetermined rotational stroke and the worm wheels 34 and 34' continue to rotate even during loading. Therefore, a considerably large part .theta..sub.1 of the rotational driving stroke of the worm wheels is used for the driving of the loading mechanism and only a small part .theta..sub.2 of the rotational stroke is available for the driving of the operation mechanism. More specifically, assuming that the maximum angle of rotation of the worm wheels is 360.degree., there is a relationship expressed by: EQU .theta..sub.2 =360.degree.-.theta..sub.1, .theta..sub.2 &lt;.theta..sub.1
Thus, since various operation mechanisms such as the braking mechanism, pinch roller mechanism and so forth have to be driven within a small angular range .theta..sub.2, it is necessary to increase the precision of the mechanisms because it would otherwise be difficult to have an accurate and reliable change-over from one mode to another.